KR20210045408A - Selective catalytic reduction process and method of regenerating the deactivated catalyst of the process - Google Patents

Abstract

A process for the regeneration of a deactivated nitrogen oxide cracking catalyst used for the selective catalytic reduction of nitrogen oxides contained in a flue gas stream is presented.

Description

Selective catalytic reduction process and method of regenerating the deactivated catalyst of the process

Non-Temporary Applicant The present invention claims priority to pending U.S. Provisional Application Serial No. 62/721,247 filed August 22, 2018, the entire disclosure of which is incorporated herein by reference.

Technical field

The present invention relates to a catalytic process for removing nitrogen oxides and sulfur oxides from a hot process gas stream containing nitrogen oxides and sulfur oxides, and regenerating the deactivated catalyst of the process.

Carbon monoxide, carbon dioxide, nitrogen oxides, sulfur compounds and other pollutants from the combustion of fuel sources such as coal, oil, gas, wood, municipal waste, industrial waste, hospital waste, hazardous waste and agricultural waste in furnaces or boilers Hot flue gases are produced that contain combustion products such as. Some of these other contaminants include particulates. The particulates may include fly ash, dust, soot, and other fine particulate matter that may include phosphorus, heavy metals, alkali metals and alkaline earth metals. _{The nitrogen oxides (NO x} ) contained in the hot flue gas stream include nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ). Sulfur compounds include sulfur oxides (SO _x ), such as disulfide oxides (SO ₂ ) and trisulfur oxides (SO ₃ ). Sulfur compounds arise from the presence of sulfur in the combustion fuel.

_{A common method of removing NO x} from the flue gas stream of a combustion process is a selective catalytic reduction (SCR) process. This process relates to catalytic reduction of _{NO x} to nitrogen (N ₂ ) and water (H ₂ O) by a reaction between _{NO x} and ammonia (NH ₃ ) in a catalyst bed. The main reaction of the SCR process is presented as follows:

4 NO + 4 NH ₃ + O ₂ → 4 N ₂ + 6 H ₂ O

2 NO ₂ + 4 NH ₃ + O ₂ → 3 N ₂ + 6 H ₂ O

NO + NO ₂ + 2 NH ₃ → 2 N ₂ + 3 H ₂ O

6 NO ₂ + 8 NH ₃ → 7 N ₂ + 12 H ₂ O

The catalyst layer usually comprises a catalytically active material, such as a nitrogen oxide decomposition catalyst, also referred to herein as a deNOx catalyst, which is a metal oxide and a catalytically active metal component such as titanium, tungsten, molybdenum, vanadium, or nitrogen oxide. Other suitable compounds known to catalyze the conversion of from to nitrogen and water. Examples of catalytically active materials are vanadium pentoxide (V ₂ O ₅ ) and tungsten trioxide (WO ₃ ).

One problem with the use of denitrification oxide catalysts in SCR processes for treating combustion flue gas streams is that over time they are contaminated by the decomposition of particulates and the reaction products of ammonia and sulfur compounds in the hot flue gas stream. Is that it becomes inactive and inactive. These products include, for example, ammonium sulfate and ammonium disulfate. In addition, other ammonium salts, such as ammonium chloride and ammonium nitrate, are formed by reaction of the injected ammonia with the components in the flue gas stream and may be deposited on the denitrification oxide catalyst. When the denitrification oxide catalyst is deactivated due to the decomposition of the ammonium salt, it is necessary to regenerate the catalyst to recover at least some of its lost activity.

US 8,883,106 describes one method of regeneration of a denitrification oxide catalyst. This patent presents a selective catalytic reduction reactor system for removing nitrogen oxides and sulfur oxides from hot process gases. The reactor system has a structural feature that provides an on-line process to regenerate its catalytic elements. The system includes a number of catalyst bed segments arranged in parallel with the flow of hot process gas treated by the use of the system. This patent further discloses a method of regenerating a catalyst bed segment. The regeneration method comprises the steps of separating one of the catalyst bed segments from the stream of hot process gas, and regeneration through the separated catalyst layer segment while the other catalyst layer segment is used simultaneously to remove nitrogen oxides and sulfur oxides from the hot process gas And delivering the gas.

EP 2 687 283 describes another method of regeneration of a denitrification oxide catalyst. This publication shows a gas treatment system or installation used to remove nitrogen oxides from a gas stream by catalytic reduction of nitrogen oxides contained in the gas stream. The gas treatment system includes a reactor system having a plurality of separate reactors or compartments including a catalyst, configured to regenerate the catalyst of an individual reactor or compartment while using another reactor or compartment including a catalyst when treating a gas stream. do. The system further comprises a desalination/desulfurization unit located upstream of the reactor system to treat the gas stream. The system also includes a gas treatment circuit and a regeneration circuit. The gas treatment circuitry supplies the gas stream to the catalyst module of the reactor system or denitrifies the gas stream by supplying it through the catalyst module, while the regeneration circuitry circulates the regeneration gas through its other catalytic module, thereby partially reducing the catalyst of the reactor system. Regenerate. The regeneration off-gas is combined with the gas stream supplied to the desalination/desulfurization process.

Some of the problems with these prior art flue gas catalytic denitrification systems providing an on-line method of catalyst regeneration arise in systems with equipment of a structure comprising separate reactors or compartments. These separate reactors or compartments are separated from each other, and when the flue gas stream is processed, the remaining reactors or compartments are used and simultaneously regeneration in a single reactor or compartment is possible. These regeneration methods require separate reactors or compartments, as well as complex structural features including expensive and difficult to use and control valve and switch systems.

There has been a continuing desire to provide an improved catalytic gas treatment system that is easy to use and less costly than many systems of the prior art.

Accordingly, a process is provided for selective catalytic reduction of nitrogen oxides contained in a gas stream, and for regeneration of deactivated SCR catalysts. This process provides a processed flue gas stream containing nitrogen oxides and sulfur compounds, which has an upstream inlet and a downstream outlet and is passed to the SCR system containing the SCR catalyst. The processed flue gas stream is contacted with the SCR catalyst for a time sufficient to provide a deactivated SCR catalyst deactivated by the sulfur compounds. The denitrified flue gas stream is obtained from the SCR system for discharge into the stack. The delivery of the processed flue gas stream to the SCR system is then stopped by isolating the SCR system, providing a closed system. After filling the closed system with processed flue gas, a portion of the processed flue gas stream is the regeneration gas used to regenerate the deactivated SCR catalyst to obtain the regeneration exhaust gas containing SOx and ammonia, the rate of introduction into the closed system. Is introduced as. Some or all of the regeneration exhaust gas circulates from the downstream outlet of the SCR system to the upstream inlet at a circulation rate. A portion of the processed flue gas stream is simultaneously introduced into the closed system while a portion of the regeneration off-gas is removed from the closed system at a rate of removal.

1 is a schematic flowchart illustrating an embodiment of the process of the present invention.

The present invention provides a process for treating combustion flue gases produced by combustion of a fuel source in a furnace or boiler prior to delivery to the flue-gas stack for discharge of the combustion flue gas to the outside atmosphere. Conventional flue gas streams produced by furnaces or boilers contain oxides of nitrogen, oxides of sulfur and particulates, which need to be reduced before the flue gas stream is released to the atmosphere.

The flue gas treatment system may comprise a system in which several different types of treatment units used to remove the different contaminants contained in the flue gas stream are integrated. These include an acid gas removal unit that removes acid gases such as sulfur oxides (SO ₂ and SO ₃ ) and HCl from the flue gas stream to provide a desulfurized flue gas stream, and a flue processed by removing particulates from the flue gas stream. A particulate removal unit may be included that provides a gas stream.

The processed flue gas stream contains nitrogen oxides formed by combustion in a furnace or boiler of the fuel source and is discharged together with the combustion flue gas stream. Thus, the processed flue gas stream comprises nitrogen oxides such as N ₂ O, NO, NO ₂ and any combination thereof, and unremoved sulfur oxides and particulates. The processed flue gas stream can be delivered to a selective catalytic reduction (SCR) system, which _{catalyzes NO x} to N ₂ and water _{by reaction of NO x} and injected ammonia or urea in the NOx catalyst bed. It provides a means for removing nitrogen oxides by reduction.

The flue gas treatment system may also include treatment of the flue gas of combustion by selective non-catalytic reduction of nitrogen oxides. This is done upstream of the SCR system and involves introducing ammonia or urea into the boiler at a location where the temperature of the hot flue gas in the boiler is in the range of 760°C (1400°F) to 1090°C (1994°F). At these temperatures, urea decomposes into ammonia, and nitrogen oxides react with ammonia and oxygen to form molecular nitrogen and water. The efficiency of selective non-catalytic reduction is typically low, so that the conversion range of nitrogen oxides contained in the hot flue gas can be 5% to 50%.

Regardless of whether the hot flue gas stream exiting the boiler is treated by selective non-catalytic reduction or not by selective non-catalytic reduction, the hot flue gas stream contains nitrogen oxides, sulfur compounds and other pollutants. Contains concentrations of combustion products. The concentration of nitrogen oxides in the hot flue gas stream may range from 50 ppmw to 5,000 ppmw. However, more generally, the concentration of nitrogen oxides in the hot flue gas stream may range from 75 ppmw to 2,000 ppmw. The hot flue gas stream may have a concentration of sulfur compounds in the range of 35 ppmw to 350 ppmw, or more typically 200 ppmw to 4.000 ppmw. The amount of particulate matter contained in the hot flue gas stream is generally 0 mg/m ³ to 30,000 mg/m ³ in the flue gas stream under standard pressure and temperature conditions, but more typically 5,000 mg/m ³ to 20,000 mg /m ^{3 in} the range.

A hot flue gas stream comprising at least one acid gas component, such as sulfur dioxide and sulfur trioxide (SO ₂ and SO ₃ ), is produced from a furnace or boiler to treat the flue gas stream to remove at least some of its acid gas components. It is delivered to the degassing unit or system. Thus, the acid gas removal unit of the process provides a means or method for removing at least some of the acid gas components contained in the flue gas stream from the flue gas stream.

Any suitable acid gas removal unit known to those skilled in the art can be used to remove the acid gas component from the flue gas stream. The conventional method for removing acid gases, in particular sulfur dioxide and sulfur trioxide, as well as other acid gas components such as hydrogen chloride from the flue gas stream, is by wet scrubbing and drying or semi-drying processes. These processes use either a dry alkaline absorbent or a solution of alkaline absorbent or a slurry of solid alkaline absorbent to remove sulfur dioxide, sulfur trioxide and other acid gas components from the flue gas stream. Alkaline absorbents suitable for the treatment of slurries or solutions include calcium carbonate (CaCO ₃ , limestone), calcium hydroxide (Ca(OH) ₂ slaked lime), magnesium hydroxide (Mg(OH) ₂ ) and caustic soda (NaOH). Can be selected from a group.

In a wet dust collection and semi-dry treatment method for removing acid gas, the flue gas stream is contacted with a slurry or solution of an alkaline absorbent under conditions suitable for removing sulfur from the flue gas stream. Typically, the method uses a vessel defining the contact area, in which the absorbent slurry or solution is in the same direction as the flow of the flue gas stream introduced into the contact area of the tube, countercurrently or crosswise. It is sprayed with. The sulfur in the flue gas stream reacts with an alkaline absorbent that removes at least a portion of the sulfur content in the flue gas stream to obtain a desulfurized flue gas stream.

Another suitable method of removing acid gas from the flue gas stream includes the so-called drying method. In a suitable dry treatment method of the present invention, an alkaline substance in powder form, such as sodium bicarbonate (NaHCO ₃ ), is contacted with the flue gas stream in a defined contact area by means of a tube or any other suitable contacting means. The acid gas of the flue gas stream reacts with alkaline substances within the contact area of the tube to form solid salts removed from the contact area.

_{The amount of SO 2} contained in the flue gas stream removed by the acid gas removal unit ranges up to 85% or up to 95%, or even up to 95% or 99% of _{the SO 2} contained in the flue gas stream. Can be _{Typically, the amount of SO 2} removed from the flue gas stream can range from 10% to 80%, and more typically, the SO ₂ removal ranges from 30 to 75%.

Wet acid gas removal systems require an upstream particulate removal system, whereas semi-dry and drying systems do not require an upstream particulate removal system, which will be installed downstream of the acid gas removal unit. In either case, the flue gas stream is delivered to a particulate removal unit or system to remove at least some of the particulate matter contained in the flue gas stream. A particulate removal unit is a filtering device that provides a means and method for removing particles from the flue gas stream to obtain a processed flue gas stream that is delivered to the SCR system. SCR is installed downstream of both the particulate removal unit and the acid gas removal unit.

Any suitable particulate removal system known to those skilled in the art is used to remove particulate matter from the flue gas stream. Thus, particulate matter is removed by any suitable particulate removal means or method. However, typical systems include electrostatic precipitator and baghouse filter systems. The electrostatic settling device removes particles from the flue gas stream by applying an electrostatic force, separating the particles contained in the flue gas stream. Filter dust collector systems use woven or felt fibrous material as filter media to remove particulates.

The particulates contained in the flue gas stream mostly range in size from 0.5 microns (μm) to 300 microns (μm), with more than 70 wt.% of the particles, more particularly 70 to 98 wt.% of the particles being 0.5 μm to 300 μm. It has a particle size in the μm range. The filter dust collector system can remove as much as 99% or more of the particulates contained in the flue gas stream, thereby providing a processed flue gas stream of the flue gas treatment process. Typically, the percentage of particulates removed from the flue gas stream ranges from 80% to 99.9% of the particulates, providing a processed flue gas stream ready to be processed by a selective catalytic reduction (SCR) system.

The process of the present invention not only includes the selective catalytic reduction of nitrogen oxides contained in the processed flue gas stream, by the use of an SCR system, but it also includes the deactivated denitrification oxide catalyst of the SCR system of the flue gas treatment process, i.e. It further includes a novel method of regenerating the SCR catalyst. The SCR system is a component of a system in which treatment units including an acid gas treatment unit and a particulate removal unit are integrated to process the flue gas stream prior to discharge to the atmosphere.

The SCR catalyst of the SCR system may be any denitrification oxide catalyst or catalyst system known to those skilled in the art, which is a nitrogen oxide compound contained in the flue gas stream by reaction of a nitrogen oxide compound and ammonia. And water catalyzed reduction. The SCR system includes an SCR catalyst selected from a variety of denitrification oxide catalyst compositions having any suitable structural shape or shape.

The SCR catalyst or denitrification oxide catalyst may include a base metal catalyst, which typically includes titanium oxide or vanadium oxide as a carrier. The carrier may further contain other metal oxides. The carrier may also have any suitable shape or structure, such as a honeycomb structure, or a ceramic metal or foam structure, or it is agglomerates such as extrudates, pills and balls. The denitrification oxide catalyst may further include one or more active metal components selected from the group of metals consisting of vanadium, tungsten and molybdenum. Other denitrification oxide catalyst compositions may be zeolite-based, typically used in high temperature applications, and the denitrification oxide catalyst compositions may be noble metal catalysts for use in low temperature applications.

U.S. Patent No. 6,419,889 discloses suitable denitrification oxide catalyst compositions useful for the SCR catalyst of the process of the present invention. This patent is incorporated herein by reference. It describes titania extrudate particles impregnated with one or more active denitrification oxide metals, such as vanadium, molybdenum and tungsten, which can suitably be used as the SCR catalyst of the present invention.

Examples of suitable ceramic or metallic foam denitrification oxide catalysts useful as SCR catalysts in the process of the present invention include those described in WO 2017/112615. This publication is incorporated herein by reference. The ceramic foam is prepared by filling the pores of the foamed polymer with an aqueous slurry of ceramic material, and drying and calcining the wet foam so that the polymer is vaporized or burned. The metallic foams are produced by a powder metallurgy process that converts nickel or iron foams into high temperature alloys. Suitable active denitrification oxide metals described herein are incorporated into ceramic or metal foams.

U.S. Patent No. 8,758,711 provides examples of suitable honeycomb structures and denitrification oxide catalyst compositions. This patent is incorporated herein by reference. These catalysts comprise a honeycomb structured carrier having a plurality of through-holes providing a reaction flow path. The carrier may further include an oxide compound of at least one element selected from the group consisting of Si, B, P, Zr and W. The active denitrification oxide metal selected from the group consisting of _{V 2} O ₅ , WO ₃ and MoO _{3 is incorporated into the honeycomb carrier.}

The SCR system is any system that can be integrated into the flue gas processing system and can perform the functions described herein. The SCR system receives a processed flue gas stream comprising nitrogen oxides and sulfur compounds, delivered from a particulate removal unit. SCR systems provide a means and method for removing nitrogen oxides from the processed flue gas stream to obtain a denitrified flue gas stream, which is preferably discharged to the stack.

The SCR system has an upstream inlet for receiving a processed flue gas stream, and a downstream outlet for discharging the denitrified flue gas stream. The SCR system defines a contact area containing a denitrification oxide catalyst as described above. Ammonia or urea is introduced into the processed flue gas stream and mixed with it, which is transferred to and introduced into the contact area of the SCR system, where it is a reaction condition in which nitrogen oxides in the processed flue gas stream are catalytically reduced to nitrogen and water. Under the reduction of nitrogen oxides, i.e. denitrification oxides, they are contacted with the SCR catalyst.

Suitable denitrification oxide reaction conditions include a reaction pressure in the range of -10 kPa (gauge) to 2000 kPa (gauge), and a reaction or contact temperature in the range of 130°C to 450°C. In normal operation of the SCR system for removing or reducing NOx contained in the processed flue gas stream, the space velocity is 3,000 hr ^-1 to 100,000 hr ^-1 , more typically 3,000 hr ^-1 to 50,000 hr ^-1 , the most Usually, it is in the range of ^{5,000 hr -1} to 20,000 hr ^-1.

The SCR system is operated as part of the process of the present invention comprising delivering the processed flue gas stream to the SCR system, and introducing it through an upstream inlet into the contact area of the SCR system. The denitrification flue gas with a reduced nitrogen oxide concentration compared to the processed flue gas stream is obtained from the SCR system through the downstream outlet of the SCR system and is discharged to the stack and to the atmosphere. The processed flue gas stream is contacted with the SCR catalyst for a time sufficient to provide a deactivated SCR catalyst. The SCR catalyst is deactivated by sulfur compounds through the mechanism described above.

The typical contact time for deactivation of the SCR catalyst is in the range of 1 to 16,000 hours, more typically the contact time is in the range of 200 to 8,000 hours. These deactivation times are for the typical space velocities required to process the processed flue gas stream.

Once the SCR catalyst is deactivated to the extent that it no longer removes nitrogen oxides from the processed flue gas stream to an acceptable or desired level, the delivery of the processed flue gas stream to the SCR system is stopped, or due to separation of the SCR system. Discontinuous to provide a closed system. The deactivated SCR catalyst of the isolated SCR system is then regenerated.

The SCR system is isolated by any suitable means or method known to those skilled in the art. Preferably, it blocks the gas flow in the conduit providing gas exchange between the upstream inlet of the SCR system and the other treatment units of the flue gas processing system, and between the downstream outlet of the SCR system and the stack of the flue gas processing system. It is achieved by blocking the gas flow in the conduit to provide a. Upstream damper or valve means are provided to block or stop the flow of the processed flue gas stream to the SCR system, and downstream damper or valve means block or stop the flow of the denitrified gas stream from the SCR system to the stack or atmosphere. It is provided to do.

In one embodiment of the process of the present invention, regeneration of the deactivated SCR catalyst comprises diverting the processed flue gas stream as a bypass stream to the stack of the flue gas processing system, around a closed system made by isolation of the SCR system. do. One advantage of the process of the present invention is that it provides regeneration of the SCR catalyst without the need to shut down the operation of the furnace or boiler, and other elements of the flue gas processing system. The deactivated SCR catalyst can then be regenerated, during which the processed flue gas stream is simultaneously delivered to the stack.

To regenerate the deactivated SCR catalyst, the closed system is first charged with regeneration gas from the processed flue gas process stream. The regeneration gas circulates at a circulation rate through the closed system and is sent to the deactivated SCR catalyst to regenerate the deactivated SCR catalyst to obtain a regeneration exhaust gas containing SOx and ammonia, which is a regeneration product derived from the deactivated SCR catalyst.

In order to remove the regeneration products from the circulating regeneration effluent gas of the closed system, a portion of the circulating regeneration effluent gas is removed from the closed system as a bleed or slip stream, during which the processed process bypasses the closed system. A portion of the flue gas stream is simultaneously introduced into the closed system as new regeneration gas.

One advantage of the inventive process for regenerating deactivated SCR catalysts is that they provide an energy efficient regeneration process that requires less energy use than many other methods of regeneration. The temperature of the regeneration gas required for regeneration of the deactivated SCR catalyst is higher than that of the processed flue gas stream of the SCR system, but since the regeneration gas circulates in a closed system, the minimum amount of incremental heat inflow is required to maintain the regeneration temperature of the circulating gas. (incremental heat input) is required. The required incremental heat input increases the temperature of a portion of the processed flue gas stream introduced into the closed system to the temperature of the circulating regeneration gas in the closed system, and approaches the degree to which heat losses need to be compensated.

In a preferred embodiment of the regeneration method of the present invention, a portion of the processed flue gas stream is continuously introduced or fed into the closed system as regeneration gas. This regeneration gas is introduced into the SCR system through its upstream inlet, sent to the deactivated SCR catalyst, and regenerated. The regeneration off-gas, including the regeneration products of SOx and ammonia, is delivered from the SCR system via its downstream outlet and circulates at a circulation rate throughout the closed system from the downstream outlet to the upstream inlet.

In order to remove the regeneration products from the circulating regeneration exhaust gas, a portion of the regeneration exhaust gas is removed from the closed system at a removal rate sufficient to continuously remove the regeneration products from the circulating regeneration exhaust gas of the closed system. It is preferred to deliver the discharged recycle effluent gas as a recycle stream and feed component to an acid gas removal unit. In this case, the discharged regeneration exhaust gas is delivered from the closed system to the acid gas removal unit and is introduced as a feed together with the flue gas stream which is charged to the acid gas removal unit.

It is desirable to control the amount of processed flue gas stream continuously introduced or supplied to the closed system by flow control, and also to control the rate of removal of the circulating regeneration off-gas by flow control, provided that the rate of removal does not reduce the regeneration product. Sufficient for continuous removal, but not high enough to exceed the capacity of the acid gas removal system to be supplied. However, any suitable means or method may be used to control the rate at which processed flue gas is supplied or introduced into the closed system, and to control the rate at which regeneration off-gas from the closed system is removed.

As mentioned above, the regeneration temperature of the circulating regeneration off-gas is maintained at a temperature higher than that of the processed flue gas stream introduced into the closed system. The regeneration temperature needs to be above 220° C., and typically it is in the range of 220° C. to 500° C., preferably 275° C. to 400° C. Thermal energy is introduced into the circulating regeneration gas by direct heat exchange or indirect heat exchange with a heat source to maintain or control the regeneration temperature.

The process of the present invention provides a reduced volume of processed flue gas that is delivered to the deactivated SCR catalyst, thereby restoring catalytic activity compared to, for example, a once-through regeneration process. In order to increase the space velocity and improve the regeneration efficiency of the process of the present invention, instead of applying the conventional method using fresh processed flue gas as a one-time or single-pass regeneration gas, a deactivated SCR catalyst All of the regeneration gas portion through is recycled. Combining the reduction of the volumetric flow of fresh processed flue gas delivered to the deactivated SCR catalyst with recirculation of the regeneration gas reduces the energy required compared to a one-time or single pass (pas) regeneration.

Thus, the space velocity through the SCR system of the circulating recycled off-gas must be slower than the typical space velocity of the processed flue gas stream while using the SCR system for the denitrification oxide treatment. Therefore, the regeneration space velocity of the circulating regeneration exhaust gas ^{should be less than 3,000 hr -1} , preferably, it is ^{less than 2,500 hr -1} and even less than 2,000 hr ^-1 . Thus, the reproduction space speed is typically in the range of 10 hr ¹ to 3,000 hr ^-1 , or 10 hr ^-1 to 2,500 hr ^-1 or 2,000 hr ^-1 . The regeneration pressure in the closed system can range from -10 kPa to 2,000 kPa.

The regeneration gas circulates throughout the closed system for a cycle time sufficient to regenerate the deactivated SCR catalyst by recovering at least a portion of its reduced activity. The cycle time can range from 10 hours to 240 hours. More typically, the cycle time can range from 20 hours to 100 hours.

Once sufficient activity has been restored to the deactivated SCR catalyst, the introduction of the processed flue gas into the closed system is stopped, and regeneration is stopped by removing the regeneration exhaust gas from the closed system. Thereafter, the closed system is reopened and the processed flue gas stream is passed back to the SCR system and processed for removal of nitrogen oxides to obtain a denitrified flue gas stream.

1 presents a process flow diagram illustrating an embodiment of a process system 10 of the present invention that provides for the treatment of flue gases produced by a furnace or boiler 12. The furnace 12 defines a combustion zone 14 and a heat transfer zone 16 and provides a means for burning or burning a fuel source. The fuel source is introduced via line 18 into the combustion zone 14 and combustion air is introduced via line 20. Combustion produces a hot flue gas stream to be discharged from the furnace 12 through line 24. The flue gas stream contains oxides of nitrogen, oxides of sulfur and particulates.

The combustion flue gas can be treated by applying a selective non-catalytic reduction reaction in the furnace 12 for the removal of nitrogen oxides in the furnace 12. To achieve this, ammonia or urea is introduced via line 26 into either the combustion zone 14 or the heat transfer zone 16 at a location where ^{the temperature of the hot flue gas ranges from 760 o} C to 1,000 ^{o C.} do.

The flue gas stream delivered via line 24 is introduced into an acid gas removal unit 30. In this embodiment of the process of the present invention, the acid gas removal unit 30 first processes the hot flue gas to obtain a desulfurization flue gas stream prior to the further process of removing particulates from the desulfurization flue gas stream. In an alternative embodiment of the process of the present invention, the sequence of flue gas treatment is reversed so that the hot flue gas is first treated by a particulate removal unit to remove particulates and provide a cleaned gas stream, which is then transferred to an acid gas removal unit. Treatment to provide a desulfurized flue gas stream or a processed flue gas stream. In certain embodiments, the acid gas removal unit 30 is a type known in the art as a dry or semi-dry acid gas removal system, which can be used to inject the absorbent in dry or slurry form. Application of this type of treatment system yields a desulfurized gas stream in which no moisture is added to the flue gas or in a minimal amount, except where it can be introduced by evaporation of the alkaline absorbent slurry. In an alternative embodiment, the type of acid gas removal unit is a wet scrubber that is delivered from the acid gas removal unit stream at its dew point to obtain a saturated desulfurized flue gas.

The acid gas removal unit 30 defines an acid gas removal region 32 in which the flue gas stream contacts a slurry or dry powder of an alkaline absorbent. The acid gas removal unit 30 is for contacting the slurry or dry powder of the alkaline absorbent introduced into the acid gas removal region 32 via the line 36 and the flue gas stream of the line 24 containing the acid gas. Provides a means. The reaction product of the alkaline absorbent and the acid gas is delivered via line 38 from the acid gas removal unit 30 for further processing or disposal. Some of the reaction products not recovered by the acid gas removal unit 30 may be delivered to the particulate removal unit 44 along with the desulfurization gas stream.

The treatment of the flue gas stream by the acid gas removal unit 30 is transferred from the acid gas removal unit 30 via the line 40 and introduced into the particulate removal area 42 defined by the particulate removal unit 44. A desulfurized flue gas stream is obtained. The particulate removal unit 44 provides a means of removing particulates including reaction products from the acid gas removal unit 30 from the desulfurized flue gas stream, thereby obtaining a processed flue gas stream having a reduced particulate concentration. The particulate reaction product removed from the acid gas removal unit 30 is delivered from the particulate removal unit 44 via a line 48.

The processed flue gas stream is delivered from the particulate removal unit 44 through a conduit 50, where ammonia is introduced via line 52 and prior to sending the mixture to the SCR system 54, the processed flue gas. Mixed with the stream. The SCR system 54 provides a means for catalytic reduction of nitrogen oxides contained in the processed flue gas stream to molecular nitrogen and water.

The SCR system 54 includes a structure defining a contact region 56, which includes a denitrification oxide catalyst 58. The denitrification oxide catalyst 58 may be included within the module, which may be combined directly with other structural elements of the SCR system 54, or provides a flow of the processed flue gas stream across the denitrification oxide catalyst 58, and It provides for contact of the processed flue gas stream with the denitrification oxide catalyst 58.

The SCR system 54 comprises an upstream inlet 60 receiving a feed gas, such as a processed flue gas stream comprising nitrogen oxide compounds, and a processed process stream, such as a processed processed flue gas stream or from the SCR system 54. It has a downstream outlet 62 for discharging and harvesting the denitrified flue gas stream.

The processed flue gas stream is introduced into a contact zone 56, where it is contacted with a denitrification oxide catalyst 58 under suitable denitrification oxide reaction conditions to obtain a denitrified flue gas stream. The denitrified flue gas stream is sent from the contact area 56 through conduit 66 to the stack 68.

The processed flue gas is contacted with the denitrification oxide catalyst 58 for a contact time sufficient to provide a deactivated SCR catalyst 58 that is deactivated by the sulfur compound. Once the denitrification oxide catalyst 58 is sufficiently deactivated, charging of the processed flue gas stream to the SCR system 54 is stopped, and the SCR system 54 is isolated, providing an isolated or closed system 69. do.

To isolate the SCR system 54, an upstream damper or valve means 70 is inserted into the conduit 50 at a location between the outlet of the particulate removal unit 44 and the upstream inlet 60 of the SCR system 54. The downstream damper or valve means 74 is inserted into the conduit 66 at a location between the stack 68 and the downstream outlet 62 of the SCR system 54. Both the upstream damper 70 and the downstream damper 74 are closed to block gas flow exchange to and from the SCR system 54, providing a closed system 69. . The circulation line 76 provides flow exchange from the downstream outlet 62 to the upstream inlet 60, allowing circulation flow within the closed system 69.

Bypass line 80 provides a flow of processed flue gas streams from particulate removal unit 44 to SCR system 54 and closed system 69. The bypass line 80 is from the conduit 50 located between the outlet of the particulate removal unit 44 and the inlet of the upstream damper 70, and the conduit between the outlet of the downstream damper 74 and the stack 68. Provides gas flow transfer to (66). When the SCR system 54 is isolated by closing both the upstream damper 70 and the downstream damper 74, the processed flue gas stream exits the particulate removal unit 44, resulting in the SCR system 54 and the closed system 69. ) To the conduit 66 and stack 68 via line 80.

Regeneration of the deactivated SCR catalyst 58 involves filling the closed system 69 with processed flue gas, which acts as a regeneration gas used to regenerate the deactivated NOx catalyst 58. Line 82 provides fluid flow transfer from conduit 66 to circulation line 76 of closed system 69. The processed flue gas is introduced into the closed system 69 via line 82 for use as regeneration gas.

A control valve 83, which provides a means for controlling the rate at which the processed flue gas is introduced into the closed system 69, is inserted into the line 82. The flow rate of the processed flue gas introduced into the circulation line 76 of the closed system 69 is measured by a flow sensor and delivery means 84. The flow transmitter means 84 provides a signal 85 to the flow controller 86 indicative of the flow rate of the treated flue gas through the line 82. Flow controller 86 provides a differential flow rate by comparing this measured flow rate to the desired flow rate. The flow controller 86 adjusts the control valve 83 in response to the differential flow rate, so that the flow rate of the processed flue gas passed through the line 82 and introduced into the circulation line 76 of the closed system 69 is desired. To keep it.

The regeneration gas is circulated at a circulation rate through the circulation line 76 of the closed system 69, and is sent to the deactivated SCR catalyst 58 to be regenerated, to obtain a regeneration exhaust gas containing SOx and ammonia. The regeneration off-gas is delivered from the SCR system 54 through a downstream outlet 62 and is circulated through a circulation line 76 throughout the closed system.

In order to continuously remove the regeneration products in the circulating regeneration effluent gas, a bleed or slip stream is removed from the circulating regeneration effluent via line 84, delivered and introduced into line 24, Here it is combined with the flue gas stream delivered to the acid gas removal unit 30. While the processed flue gas is continuously introduced into the closed system via line 82 as regeneration gas, the bleed stream of circulating regeneration exhaust gas is simultaneously removed via line 84 from the closed system.

Once a sufficient amount of activity has been restored to the deactivated SCR catalyst 58, the introduction of the processed flue gas through line 82 into the closed system, and removal of the regeneration exhaust gas through line 84 from the closed system. By stopping, playback is stopped. Thereafter, the closed system is reopened by opening both the upstream damper 70 and the downstream damper 74, and the bypass of the processed flue gas stream around the SCR system 54 through the bypass line 80 is stopped, The processed flue gas stream is passed back to the SCR system 54 to be treated for removal of nitrogen oxides, and the denitrified flue gas stream is transferred from the SCR system 54 to the stack 68 via line 66. Get

Claims (10)

A process for selective catalytic reduction of nitrogen oxides contained in a gas stream and regeneration of deactivated catalysts, the process comprising:
Providing a processed flue gas stream containing nitrogen oxides and sulfur compounds;
The processed flue gas stream is sent to an SCR system having an upstream inlet and a downstream outlet containing an SCR catalyst, and the processed flue gas stream is transferred to the SCR catalyst for a time sufficient to provide a deactivated SCR catalyst deactivated by a sulfur compound. Contacting with and obtaining a denitrified flue gas stream for discharge from the SCR system into a stack;
Stopping said step of sending said processed flue gas stream to said SCR system by isolating said SCR system, thereby providing a closed system;
After filling the closed system with the processed flue gas, the regeneration gas used to regenerate the deactivated SCR catalyst to regenerate the SCR catalyst to obtain a regeneration exhaust gas containing SOx and ammonia, wherein the processed flue gas stream Introducing a portion of the into the closed system at an introduction rate; Circulating all or part of the regeneration exhaust gas from the downstream outlet to the upstream inlet at a circulation rate; And
And simultaneously introducing a portion of the processed flue gas stream into the closed system while removing a portion of the regeneration off-gas from the closed system at a rate of removal. The method of claim 1,
Burning the combustible material in a furnace to obtain a flue gas stream comprising nitrogen oxides, acid gas components and particulates therefrom;
Treating the flue gas stream by an acid gas removal unit to remove an acid gas component from the flue gas stream and obtaining a desulfurized flue gas stream; And
And removing particulates from the flue gas stream or the desulfurized flue gas stream by a particulate removal unit to obtain the processed flue gas stream. The method according to claim 2 or 3,
The process further comprising removing a portion of the nitrogen oxides in the flue gas stream by introducing either or both ammonia or urea into the furnace, thereby inducing a selective non-catalytic reduction of the nitrogen oxides. The method of claim 2,
The process further comprising introducing said portion of said regenerative exhaust gas to either or both of said acid gas removal unit or said particulate removal unit. The method of claim 4,
The process further comprising controlling the regeneration temperature of the regeneration gas by introducing thermal energy into the regeneration exhaust gas circulating within the closed system. The method of claim 5,
Providing a measured introduction rate by measuring the introduction rate of the part of the processed flue gas, and comparing the measured introduction rate with a desired introduction rate to provide a differential introduction rate; And
The process further comprising adjusting the introduction rate of the portion of the processed flue gas stream in response to the differential introduction rate, thereby maintaining the introduction rate at the desired introduction rate. The method of claim 6,
Providing a measured removal rate by measuring the removal rate of the part of the regenerated exhaust gas, and comparing the measured removal rate with a desired removal rate to provide a differential removal rate; And adjusting the removal rate of the portion of the regeneration exhaust gas in response to the differential removal rate, thereby maintaining the removal rate at the desired removal rate. The method of claim 7,
And sending the processed flue gas stream around the closed system as a bypass stream, and sending the bypass stream to the stack. The method of claim 8,
Measuring the circulation rate of the regeneration gas to provide a measured circulation rate, and comparing the measured circulation rate with a desired circulation rate to provide a differential circulation rate; And
The process further comprising the step of maintaining the circulation at the desired circulation rate by adjusting the circulation rate in response to the differential circulation rate. The method of claim 9,
Stopping the stopping, feeding and removing steps after the regeneration exhaust gas has been circulated for a cycle time sufficient to regenerate the deactivated SCR catalyst by recovering at least some of its reduced activity; And
The process further comprising the step of continuing the delivery step.

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